lecture 11 sexual selection

Question 1

what is intra sexual selection

Answer 1

is when members of the same sex (within a species) compete with each other in order to gain opportunities to mate with others, e.g. the male against male competition for females

Question 2

what is intersexual selection

Answer 2

members of one biological sex choose mates of the other sex to mate with

Question 3

how does intra-sexual selection favours traits that help

individuals win competitions for matings, e.g. antlers on male red deer

Answer 3

the ones with better antlers for example are the better fighters and therefore get to mate so pass on the genes for the better bigger antlers

Question 4

in basic terms why is being choosy adaptive

Answer 4

it offers evolutionary benefits if potential mates are

variable in qualities which might affect reproductive success

Question 5

three catorogies of why being choosy is adaptive

Answer 5

right species
direct
indirect

Question 6

why is getting the right species adaptive

Answer 6

hybrids are often sterile or ‘unfit’ in the evolutionary sense
- females in possible hybrid zones have undergone selection to be more choosy
than females in allopatric zones, e.g. Litoria frogs

Question 7

why is direct adaptive

Answer 7

direct benfits can be gained

Question 8

what direct benfits can be gained

Answer 8

mates may provide food (terns), parental care(great tits), nest sites, protection from other males(sheep),

Question 9

what are some indirect benefits

Answer 9

parasite resistance
	longevity
	‘sexiness’
‘Good genes’…
	…are inherited by the offspring
	…increase offspring viability

Question 10

what are some secondary sexual characteristics that influence

Answer 10

song complexity in Sedge Warblers

tail length in Long-tailed Widow Birds

Question 11

what are the two hypothesis as to why secondary sexual characteristics evolved?

Answer 11

fishers runaway hypothesis

Zahavi’s Handicap Principle or Good Genes Hypothesis

Question 12

breif exp fishers runaway hypothesis

Answer 12

traits can become elaborate if they co-evolve with female preference

Question 13

breif exp zahavis handicap principle

Answer 13

or they provide an honest signal of quality

Question 14

what questions must be answered to understand how secondary sexual characterisics

Answer 14

1. How female preferences might arise
2. How a preference and a trait may become genetically linked
3. How this might lead to a runaway process of increase in the males’ trait
4. Why males do not develop ever larger and larger traits if females would apparently prefer
   them

Question 15

how may female preference come about (with evidence)

Answer 15

sensory bias:
a louder call or larger tail may simply be spotted earlier or more noticable against the habitat (evidence: male
frogs which call as loud as possible to attract a mate because female frogs follow a simple
sound gradient when searching for a partner; a female which heads towards the loudest call
would be likely to be heading towards the nearest male.)

Arbitrary bias A bias towards a particular trait, such as tail length might exist but may be
neither costly nor beneficial until it is also linked with some selection on that trait – for
example males with slightly longer tails might be more aerodynamic in flight.

Question 16

what was malte anderssons experiment on long tailed widow birds

Answer 16

Trapped males
Shortened some tails, lengthened others, some stayed the same as controls

results: the ones with the lengthend tails got more mates and the ones with shortened tails got less mates. the control remained the same

Question 17

what was clive catchpoles study on sedge warblers

Answer 17

sampled different bits of the warblers song and put femles in choice chambers. the songs with the largest repitoir of song parts were favoured by the females

Question 18

what is linkage disequlibrium

Answer 18

the non random breeding that comes from females mating with males that they find attractive; resulting in offspring that either have that feature (male) or females that find that feature desirable

Question 19

why does fishers runaway process eventually stop

Answer 19

A trait such as tail length will vary from male to male. If females prefer the males with the longest tails, then
males will be at a mating advantage and will have a
reproductive success than short tailed males. this will continue to be a selected trait that increases over time and is stopped bt natural selection ie. if the tail gets too long it may not be able to escape predation and therefore not reproduce

Question 20

what is the flow of logic of zahavis handicap priciple

Answer 20

1) extravagent traits are a hinderance to survival
2)only high quality individuals can actually survive with the hinderance and therefore these good genes(eg parasite resistance, food finding) will be passed onto their young. which is adaptive for females to make the choice of in the first place
3)The signal is an honest one because only genuinely healthy males will be able to produce
or survive with a large signal/trait.
4)Males are, therefore, under strong sexual selection to produce as large a signal as they can
to attract females. Again, natural selection could act as a brake on an ever increasing trait
size, but additionally the males should be unable to produce a signal which suggests they
are a better male than they really are because of the cost of producing and maintaining
such a trait.

Question 21

which theory is correct

Answer 21

probably a mixture of both is the most likely explanation